Solar radiation has been shown to be harmful to human skin. Some harmful effects are seen immediately after sun exposure, such as in the case with sunburns, but in other cases, the damaging effects of solar radiation does not appear for many years post exposure.
Sun damage to the skin results from ultraviolet radiation (UVR) which reaches the surface of the earth. This UV radiation is divided in UVA and UVB. UVA (320 nm to 400 nm) contributes about 95% of the UVR, while UVB (290 nm to 320 nm) accounts for about 5%. Accordingly, topical sunscreens are formulated to contain active agents, which are able to absorb or reflect UVR having a wavelength of about 290 nm to 400 nm, and even reach beyond 400 nm into the visible spectrum at the blue light zone. These organic and physical sunscreens are classified into UV-A filters, UV-B filters, or broad spectrum filters (UV-A and UV-B functionality in a single molecule) depending on the type of radiation they absorb. UV-A sunscreens absorb radiation in the 320 to 400 nm regions of the ultra violet spectrum and UV-B sunscreens absorb radiation in the 290 to 320 nm regions of the ultra violet spectrum.
Topical sunscreen compositions are commonly used during outdoor work or leisure as a means for providing protection of exposed skin against acute and chronic adverse effects of solar radiation such as, for example, sunburn, sun exposure-related cancers, and skin photo-aging.
Many effective sunscreen preparations are sold commercially or are described in cosmetic or pharmaceutical literature. In general, sunscreen preparations are formulated as creams, lotions, sprays or oils containing as the active agent an ultra violet radiation absorbing chemical compound, or reflecting by physical compounds. As people have become more aware of the damaging effects of UVR, use of sunscreens has increased. Sun care products accounted for about 10% of the global skincare market in 2013 and the market is poised for growth of about 6.5% between 2013 and 2017. Global sun care sales reached about $8.7 billion in 2013. Research shows that consumers are highly concerned about sun damage, with 62% seeking sun protection benefits in skin care and body care products. Adding sun protection factor (SPF) to creams, lotions, and other body care products is becoming commonplace. Accordingly, it is desirable to improve sun protection formulations in terms of convenience, comfort and the duration of efficacy.
Currently, commercially available sun screen products are divided into two categories: chemical (organic) and physical. Chemical sunscreens are those which contain an active molecule which can absorb UVA and/or UVB radiation. Oxybenzone and avobenzone are examples of chemical sunscreens contained in sunscreen formulations. A pitfall of chemical sunscreens is the instability of the active ingredient when exposed to the sun. An example of a photosensitive sunscreen agent is avobenzone. Avobenzone becomes less effective as a sunscreen over time when exposed to solar radiation. Further, chemical compounds such as avobenzone degrade in the presence of some pigments, rendering the sunscreen ineffective. The mixing of chemical sun blocks with pigments can inadvertently occur when a user first applies such a sunscreen to her/his face followed by a cosmetic with pigments thereby rendering the active ingredient ineffective. Finally, some concerns have arisen regarding the safety of chemical sunscreens.
Physical sunscreens act as physical barriers which prevent UV rays to come into contact with a user's skin. Physical sunscreens primarily include titanium oxide or zinc oxide. Physical sunscreens, on the other hand, may generate free radicals that can be harmful. Further, physical sunscreens tend to be more visible. Both titanium oxide and zinc oxide type sunscreens come in a thick whitish paste that can be hard to apply and must be reapplied frequently as any sun-protecting qualities are lost when the physical layer of sunscreen is gone. Thus there exists a need for more natural sunscreen derivatives that can provide sun protection qualities and still be safe and relatively stable.
In recent years, a group of compounds known as mycosporines and mycosporine-like amino acids (MAAs) have received attention for their UV-absorbing qualities. Certain fungi produce mycosporine alone while cyanobacteria, algae, dinoflagellates, coral, and other marine organisms can produce both mycosporine and MAAs. MMAs are a family of intracellular compounds biosynthesized by the shikimate pathway for synthesizing aromatic amino acids involved in protecting aquatic organisms from solar radiation. MAAs are typically around 300 Daltons and are characterized by a cyclohexenon or cyclohexenimine chromophore. Discovered in the late 1960's, mycosporine and MAAs haven been subject of much research, and has been found to absorption range of 310 to 360 nm.
In recent years, some MAAs have received some attention as being viable sun screening agents. While MAAs have the benefit of being natural and thus less harmful than either chemical or physical sunscreens, the ability to produce and isolate enough MAAs from natural sources is time consuming and challenging. Thus, isolating enough MAAs from live organism to be placed into commercial production of sunscreen may not be economically feasible. Furthermore, attempts to produce MAAs synthetically has been unsuccessful thus far.
Disclosed herein are a new family of compounds with a two-armed cyclic structure and their syntheses, having some similarity to naturally-occurring MAAs by having a basic structure of amino acid cyclohexenone or cyclohexenimine conjugated arrangements. Yet, this family of molecules disclosed the feasible chemical structures and chemical variants that can absorb both UVA and UVB radiation. Thus, they are particularly effective and feasible as topical formulations for use as sunscreens. The sunscreen formulations described provide a stable active molecule and a topical formulation which is water soluble and provides greater comfort than current formulations when applied to the skin.